In aircraft and the like, it is common to have hydraulic circuits which are totally separated so that if one fails, the others will still function, thereby preventing total loss of control. It is also common to provide power transmission units which function to supply additional flow upon demand from one circuit to the other to maintain integrity of either circuit in the event that there is a malfunction therein, or an exceptionally high flow demand for a limited and known period of time.
Among the objectives of the present invention are to provide a power transmission unit wherein the transmission occurs readily and easily; which power transmission can be reversed; wherein there is substantially little net reaction torque; which have a lower weight; and wherein axial forces tend to cancel one another thereby facilitating construction.
In accordance with the invention, a power transmission unit comprises a housing and a cam block rotatable mounted in the housing and a pumping mechanism associated with opposed inclined surfaces of the cam block. A common shaft is rotatably mounted in the cam block and has its ends extending beyond the cam block. Each pumping mechanism includes a cylinder barrel mounted on the shaft for rotation with the shaft and having a plurality of cylinders with pistons slidable therein and operatively associated with a surface of the cam block. Each cylinder has a port opening to a valve plate provided with inlet and outlet ports in communication with inlet and outlet passages at each end of the housing. When one of the pumping mechanisms is operated as a motor, it drives the other pumping mechanism as a pump.